In a metal-oxide-semiconductor (MOS) transistor, the switching signal is generated by manipulating the current flow in channel region through applying a gate voltage on the gate electrode. As the feature size (or critical dimension, CD) of semiconductor devices becomes smaller, the degree of integration of semiconductor chips continuously increases. The ability of traditional planar MOS transistor to control channel current becomes insufficient, which leads to considerably large leakage current. That is, the so-called short-channel effects (SCE) become more severe in the traditional planar MOS transistor. Therefore, traditional planar MOS transistors are gradually replaced by transistors with a three-dimensional (3D) device structure, i.e., 3D transistors. A 3D transistor includes a variety of forms such as fin field effect transistor (FinFET). Compared to a traditional planar transistor, besides having a much lower leakage current (i.e. the SCE is suppressed), a 3D transistor also demonstrates many other advanced properties, such as better drive ability, and better anti-noise performance, etc.
Currently, the fabrication methods for 3D transistors often require using advanced tools with better capability and better performance. Such advanced tools usually need to be specially designed and reformed. Therefore, the fabrication cost for existing methods may be very high. The disclosed fabrication methods and 3D transistors are directed to solve one or more problems set forth above and other problems in the art.